On Thu, 21 May 2026 at 09:08, Shah, Tanmay <[email protected]> wrote:
>
>
>
> On 5/20/2026 10:43 AM, Arnaud POULIQUEN wrote:
> >
> >
> > On 5/20/26 16:55, Shah, Tanmay wrote:
> >>
> >>
> >> On 5/20/2026 2:44 AM, Arnaud POULIQUEN wrote:
> >>>
> >>>
> >>> On 5/19/26 19:36, Mathieu Poirier wrote:
> >>>> On Wed, Apr 29, 2026 at 09:10:52AM -0700, Tanmay Shah wrote:
> >>>>> 512 bytes isn't always suitable for all case, let firmware
> >>>>> maker decide the best value from resource table.
> >>>>> enable by VIRTIO_RPMSG_F_BUFSZ feature bit.
> >>>>>
> >>>>> Signed-off-by: Tanmay Shah <[email protected]>
> >>>>> ---
> >>>>>
> >>>>> Test done:
> >>>>> - Verify this patch works with the existing firmware
> >>>>> - Verify this patch works with the firmware that configures
> >>>>> differt tx & rx buf size
> >>>>>
> >>>>> Changes in v2:
> >>>>> - %s/sbuf_size/tx_buf_size/
> >>>>> - %s/rbuf_size/rx_buf_size/
> >>>>> - fix typo
> >>>>> - do not use ALIGN on buf size, rely on allocator
> >>>>> - make err msg more explicit, %s/vdev config:/bad vdev config/
> >>>>> - fix license and add AMD copyrights in the header virtio_rpmsg.h
> >>>>> - Assign bit 1 to VIRTIO_RPMSG_F_BUFSZ feature
> >>>>> - use __virtio32 over __u32
> >>>>> - add version field to virtio rpmsg config structure
> >>>>> - move linux/virtio_rpmsg.h to linux/rpmsg/virtio_rpmsg.h
> >>>>>
> >>>>> drivers/rpmsg/virtio_rpmsg_bus.c | 70 +++++++++++++++++++++
> >>>>> +--------
> >>>>> include/linux/rpmsg/virtio_rpmsg.h | 27 ++++++++++++
> >>>>> 2 files changed, 79 insertions(+), 18 deletions(-)
> >>>>> create mode 100644 include/linux/rpmsg/virtio_rpmsg.h
> >>>>>
> >>>>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/
> >>>>> virtio_rpmsg_bus.c
> >>>>> index e59d8cf9b975..8116d94413cc 100644
> >>>>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> >>>>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> >>>>> @@ -20,6 +20,7 @@
> >>>>> #include <linux/rpmsg.h>
> >>>>> #include <linux/rpmsg/byteorder.h>
> >>>>> #include <linux/rpmsg/ns.h>
> >>>>> +#include <linux/rpmsg/virtio_rpmsg.h>
> >>>>> #include <linux/scatterlist.h>
> >>>>> #include <linux/slab.h>
> >>>>> #include <linux/sched.h>
> >>>>> @@ -39,7 +40,8 @@
> >>>>> * @tx_bufs: kernel address of tx buffers
> >>>>> * @num_rx_buf: total number of buffers for rx
> >>>>> * @num_tx_buf: total number of buffers for tx
> >>>>> - * @buf_size: size of one rx or tx buffer
> >>>>> + * @rx_buf_size: size of one rx buffer
> >>>>> + * @tx_buf_size: size of one tx buffer
> >>>>> * @last_sbuf: index of last tx buffer used
> >>>>> * @bufs_dma: dma base addr of the buffers
> >>>>> * @tx_lock: protects svq and tx_bufs, to allow concurrent
> >>>>> senders.
> >>>>> @@ -59,7 +61,8 @@ struct virtproc_info {
> >>>>> void *rx_bufs, *tx_bufs;
> >>>>> unsigned int num_rx_buf;
> >>>>> unsigned int num_tx_buf;
> >>>>> - unsigned int buf_size;
> >>>>> + unsigned int rx_buf_size;
> >>>>> + unsigned int tx_buf_size;
> >>>>> int last_sbuf;
> >>>>> dma_addr_t bufs_dma;
> >>>>> struct mutex tx_lock;
> >>>>> @@ -68,9 +71,6 @@ struct virtproc_info {
> >>>>> wait_queue_head_t sendq;
> >>>>> };
> >>>>> -/* The feature bitmap for virtio rpmsg */
> >>>>> -#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service
> >>>>> notifications */
> >>>>> -
> >>>>> /**
> >>>>> * struct rpmsg_hdr - common header for all rpmsg messages
> >>>>> * @src: source address
> >>>>> @@ -128,7 +128,7 @@ struct virtio_rpmsg_channel {
> >>>>> * processor.
> >>>>> */
> >>>>> #define MAX_RPMSG_NUM_BUFS (256)
> >>>>> -#define MAX_RPMSG_BUF_SIZE (512)
> >>>>> +#define DEFAULT_RPMSG_BUF_SIZE (512)
> >>>>> /*
> >>>>> * Local addresses are dynamically allocated on-demand.
> >>>>> @@ -444,7 +444,7 @@ static void *get_a_tx_buf(struct virtproc_info
> >>>>> *vrp)
> >>>>> /* either pick the next unused tx buffer */
> >>>>> if (vrp->last_sbuf < vrp->num_tx_buf)
> >>>>> - ret = vrp->tx_bufs + vrp->buf_size * vrp->last_sbuf++;
> >>>>> + ret = vrp->tx_bufs + vrp->tx_buf_size * vrp->last_sbuf++;
> >>>>> /* or recycle a used one */
> >>>>> else
> >>>>> ret = virtqueue_get_buf(vrp->svq, &len);
> >>>>> @@ -514,7 +514,7 @@ static int rpmsg_send_offchannel_raw(struct
> >>>>> rpmsg_device *rpdev,
> >>>>> * messaging), or to improve the buffer allocator, to support
> >>>>> * variable-length buffer sizes.
> >>>>> */
> >>>>> - if (len > vrp->buf_size - sizeof(struct rpmsg_hdr)) {
> >>>>> + if (len > vrp->tx_buf_size - sizeof(struct rpmsg_hdr)) {
> >>>>> dev_err(dev, "message is too big (%d)\n", len);
> >>>>> return -EMSGSIZE;
> >>>>> }
> >>>>> @@ -647,7 +647,7 @@ static ssize_t virtio_rpmsg_get_mtu(struct
> >>>>> rpmsg_endpoint *ept)
> >>>>> struct rpmsg_device *rpdev = ept->rpdev;
> >>>>> struct virtio_rpmsg_channel *vch =
> >>>>> to_virtio_rpmsg_channel(rpdev);
> >>>>> - return vch->vrp->buf_size - sizeof(struct rpmsg_hdr);
> >>>>> + return vch->vrp->tx_buf_size - sizeof(struct rpmsg_hdr);
> >>>>> }
> >>>>> static int rpmsg_recv_single(struct virtproc_info *vrp, struct
> >>>>> device *dev,
> >>>>> @@ -673,7 +673,7 @@ static int rpmsg_recv_single(struct virtproc_info
> >>>>> *vrp, struct device *dev,
> >>>>> * We currently use fixed-sized buffers, so trivially sanitize
> >>>>> * the reported payload length.
> >>>>> */
> >>>>> - if (len > vrp->buf_size ||
> >>>>> + if (len > vrp->rx_buf_size ||
> >>>>> msg_len > (len - sizeof(struct rpmsg_hdr))) {
> >>>>> dev_warn(dev, "inbound msg too big: (%d, %d)\n", len,
> >>>>> msg_len);
> >>>>> return -EINVAL;
> >>>>> @@ -706,7 +706,7 @@ static int rpmsg_recv_single(struct virtproc_info
> >>>>> *vrp, struct device *dev,
> >>>>> dev_warn_ratelimited(dev, "msg received with no
> >>>>> recipient\n");
> >>>>> /* publish the real size of the buffer */
> >>>>> - rpmsg_sg_init(&sg, msg, vrp->buf_size);
> >>>>> + rpmsg_sg_init(&sg, msg, vrp->rx_buf_size);
> >>>>> /* add the buffer back to the remote processor's virtqueue */
> >>>>> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, msg, GFP_KERNEL);
> >>>>> @@ -824,6 +824,7 @@ static int rpmsg_probe(struct virtio_device *vdev)
> >>>>> int err = 0, i;
> >>>>> size_t total_buf_space;
> >>>>> bool notify;
> >>>>> + u16 version;
> >>>>> vrp = kzalloc_obj(*vrp);
> >>>>> if (!vrp)
> >>>>> @@ -855,9 +856,41 @@ static int rpmsg_probe(struct virtio_device
> >>>>> *vdev)
> >>>>> else
> >>>>> vrp->num_tx_buf = MAX_RPMSG_NUM_BUFS;
> >>>>> - vrp->buf_size = MAX_RPMSG_BUF_SIZE;
> >>>>> + /*
> >>>>> + * If VIRTIO_RPMSG_F_BUFSZ feature is supported, then
> >>>>> configure buf
> >>>>> + * size from virtio device config space from the resource table.
> >>>>> + * If the feature is not supported, then assign default buf size.
> >>>>> + */
> >>>>> + if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_BUFSZ)) {
> >>>>> + /* note: virtio_rpmsg_config is defined from remote view */
> >>>>> + version = 0;
> >>>>> + virtio_cread(vdev, struct virtio_rpmsg_config,
> >>>>> + version, &version);
> >>>>> + virtio_cread(vdev, struct virtio_rpmsg_config,
> >>>>> + txbuf_size, &vrp->rx_buf_size);
> >>>>> + virtio_cread(vdev, struct virtio_rpmsg_config,
> >>>>> + rxbuf_size, &vrp->tx_buf_size);
> >>>>> +
> >>>>
> >>>> A check is also needed to make sure the version received from the
> >>>> resource table
> >>>> is '0'.
> >>
> >> I think we should start with versaion = 1. So, can I check the version
> >> number for 1 ?
> >>
> >>>>
> >>>>> + /* The buffers must hold at least the rpmsg header */
> >>>>> + if (vrp->rx_buf_size < sizeof(struct rpmsg_hdr) ||
> >>>>> + vrp->tx_buf_size < sizeof(struct rpmsg_hdr)) {
> >>>>> + dev_err(&vdev->dev,
> >>>>> + "bad vdev config: rx buf sz = %d, tx buf sz = %d\n",
> >>>>> + vrp->rx_buf_size, vrp->tx_buf_size);
> >>>>> + err = -EINVAL;
> >>>>> + goto vqs_del;
> >>>>> + }
> >>>>> +
> >>>>> + dev_dbg(&vdev->dev,
> >>>>> + "vdev config: version=%d, rx buf sz = 0x%x, tx buf sz =
> >>>>> 0x%x\n",
> >>>>> + version, vrp->rx_buf_size, vrp->tx_buf_size);
> >>>>> + } else {
> >>>>> + vrp->rx_buf_size = DEFAULT_RPMSG_BUF_SIZE;
> >>>>> + vrp->tx_buf_size = DEFAULT_RPMSG_BUF_SIZE;
> >>>>> + }
> >>>>> - total_buf_space = (vrp->num_rx_buf + vrp->num_tx_buf) * vrp-
> >>>>>> buf_size;
> >>>>> + total_buf_space = (vrp->num_rx_buf * vrp->rx_buf_size) +
> >>>>> + (vrp->num_tx_buf * vrp->tx_buf_size);
> >>>>> /* allocate coherent memory for the buffers */
> >>>>> bufs_va = dma_alloc_coherent(vdev->dev.parent,
> >>>>> @@ -875,14 +908,14 @@ static int rpmsg_probe(struct virtio_device
> >>>>> *vdev)
> >>>>> vrp->rx_bufs = bufs_va;
> >>>>> /* and second part is dedicated for TX */
> >>>>> - vrp->tx_bufs = bufs_va + vrp->num_rx_buf * vrp->buf_size;
> >>>>> + vrp->tx_bufs = bufs_va + (vrp->num_rx_buf * vrp->rx_buf_size);
> >>>>> /* set up the receive buffers */
> >>>>> for (i = 0; i < vrp->num_rx_buf; i++) {
> >>>>> struct scatterlist sg;
> >>>>> - void *cpu_addr = vrp->rx_bufs + i * vrp->buf_size;
> >>>>> + void *cpu_addr = vrp->rx_bufs + i * vrp->rx_buf_size;
> >>>>> - rpmsg_sg_init(&sg, cpu_addr, vrp->buf_size);
> >>>>> + rpmsg_sg_init(&sg, cpu_addr, vrp->rx_buf_size);
> >>>>> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, cpu_addr,
> >>>>> GFP_KERNEL);
> >>>>> @@ -965,8 +998,8 @@ static int rpmsg_remove_device(struct device
> >>>>> *dev, void *data)
> >>>>> static void rpmsg_remove(struct virtio_device *vdev)
> >>>>> {
> >>>>> struct virtproc_info *vrp = vdev->priv;
> >>>>> - unsigned int num_bufs = vrp->num_rx_buf + vrp->num_tx_buf;
> >>>>> - size_t total_buf_space = num_bufs * vrp->buf_size;
> >>>>> + size_t total_buf_space = (vrp->num_rx_buf * vrp->rx_buf_size) +
> >>>>> + (vrp->num_tx_buf * vrp->tx_buf_size);
> >>>>> int ret;
> >>>>> virtio_reset_device(vdev);
> >>>>> @@ -992,6 +1025,7 @@ static struct virtio_device_id id_table[] = {
> >>>>> static unsigned int features[] = {
> >>>>> VIRTIO_RPMSG_F_NS,
> >>>>> + VIRTIO_RPMSG_F_BUFSZ,
> >>>>> };
> >>>>> static struct virtio_driver virtio_ipc_driver = {
> >>>>> diff --git a/include/linux/rpmsg/virtio_rpmsg.h b/include/linux/
> >>>>> rpmsg/virtio_rpmsg.h
> >>>>> new file mode 100644
> >>>>> index 000000000000..285918be68b9
> >>>>> --- /dev/null
> >>>>> +++ b/include/linux/rpmsg/virtio_rpmsg.h
> >>>>> @@ -0,0 +1,27 @@
> >>>>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>>>> +/*
> >>>>> + * Copyright (C) Pinecone Inc. 2019
> >>>>> + * Copyright (C) Xiang Xiao <[email protected]>
> >>>>> + * Copyright (C) Advanced Micro Devices, Inc.
> >>>>> + */
> >>>>> +
> >>>>> +#ifndef _LINUX_VIRTIO_RPMSG_H
> >>>>> +#define _LINUX_VIRTIO_RPMSG_H
> >>>>> +
> >>>>> +#include <linux/types.h>
> >>>>> +#include <linux/virtio_types.h>
> >>>>> +
> >>>>> +/* The feature bitmap for virtio rpmsg */
> >>>>> +#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service
> >>>>> notifications */
> >>>>> +#define VIRTIO_RPMSG_F_BUFSZ 1 /* RP get buffer size from config
> >>>>> space */
> >>>>> +
> >>>>> +struct virtio_rpmsg_config {
> >>>>> + __virtio16 version;
> >>>>> + /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
> >>>>> + __virtio32 txbuf_size;
> >>>>> + __virtio32 rxbuf_size;
> >>>>> + __virtio32 reserved[14]; /* Reserve for the future use */
> >>>>
> >>>> 66 byte for the configuratio space? I'm puzzled about the
> >>>> reserved[14], how did
> >>>> you come up with that number?
> >>
> >> I kept the reserved bytes from the original series as it is. The
> >> original series did not contain version field. With version I don't
> >> think we need reserved field at all. At best, if we want to append
> >> padding bytes, then I think __virtio16 reserved; makes sense. That will
> >> make the structure aligned to 4 byte.
> >>
> >>>
> >>> Is it useful to define the reserved field?
> >>
> >> I think reserved field is only useful to keep the structure size aligned
> >> to 4 bytes.
> >>
> >>> The version should allow us to determine the content.
> >>
> >> Correct, but I think the structure can be aligned if used correct
> >> reserved bytes.
> >>
> >>> An other solution is to introduce a'size' field to determine the size of
> >>> the structure:
> >>
> >> I think, the resource table already contains config_len field which is
> >> size of the structure:
> >>
> >> https://github.com/torvalds/linux/
> >> blob/27fa82620cbaa89a7fc11ac3057701d598813e87/include/linux/
> >> remoteproc.h#L275
> >
> >
> > The resource table is the solution for the remoteproc virtio backend,
> > The solution should be able to work with some other virtio backends.
> > In such case we can not rely on the resource table.
> >
>
> For now we have only the remoteproc virtio backend. If we ever introduce
> new backend, then can we update this structure with new 'version' num
> and include size field at that time? Since, now there is no real use of it.
>
> > The resource table is a solution for the remoteproc virtio backend.
> > However, the solution should also be able to work with other virtio
> > backends.
> > In that case, it may not be possible to rely on the resource table.
> >
>
> Another concern is, do we need the size of the structure in the
> first-place even to retrieve the 'size' field from the structure or
> verify the integrity of the structure?
>
> For example:
> https://github.com/torvalds/linux/blob/27fa82620cbaa89a7fc11ac3057701d598813e87/drivers/remoteproc/remoteproc_virtio.c#L301
>
>
> Here to verify the integrity of the resource table, we are using virtio
> config space size.
>
> If we do then it's better to provide the 'size' field some other way
> before parsing of the rpmsg config space in any virtio backend. Like in
> the remoteproc virtio backend it's provided via the resource table.
>
> Let me know if I am overthinking :-) and we want the 'size' field in the
> config space. I am just trying to make it as minimal as possible.
I think it is better to have a 'size' field in the structure.
>
> Thanks,
> Tanmay
>
> > Regards,
> > Arnaud
> >
> >>
> >>> struct virtio_rpmsg_config {
> >>> __virtio16 version;
> >>> __virtio16 size; /* size of the configuration space */
> >>> /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
> >>> __virtio32 txbuf_size;
> >>> __virtio32 rxbuf_size;
> >>> __u8 private[0]; /* customized config */
> >>
> >> Do we need customized config? I think I should remove this comment from
> >> the original patch as well.
> >>
> >> Thanks,
> >> Tanmay
> >>
> >>> };
> >>>
> >>>>
> >>>> The rest looks good to me.
> >>>>
> >>>
> >>> Looks good to me too.
> >>>
> >>> Thanks,
> >>> Arnaud
> >>>
> >>>>> + /* Put the customize config here */
> >>>>> +} __packed;
> >>>>> +
> >>>>> +#endif /* _LINUX_VIRTIO_RPMSG_H */
> >>>>> --
> >>>>> 2.34.1
> >>>>>
> >>>
> >>
> >
>
